1. Field of the Invention
The present invention generally relates to fuel supply systems and vehicles. More particularly, the present invention relates to a fuel supply system for supplying fuel to an engine, and a vehicle equipped with the fuel supply system.
2. Description of the Related Art
A conventional fuel injector generally is located downstream (in an airflow direction) of a throttle valve. In most arrangements, an air cleaner is positioned on an opposite side of the throttle valve from the fuel injector. Thus, air is drawn into a combustion chamber of an engine through the air cleaner, across the throttle valve and past the fuel injector.
Such a construction undesirably places the fuel injector relatively close to the combustion chamber. Because the fuel injector is positioned close to the combustion chamber, the fuel injected from the fuel injector may flow into the engine without being fully atomized. Therefore, to improve fuel atomization, a second fuel injector can be positioned such that the throttle valve is positioned between the second fuel injector and the first fuel injector.
When the engine is operating under high speed and high load conditions, the second fuel injector can supply sufficient fuel to account for fuel that is not being atomized from the first fuel injector. Thus, in such a fuel supply system, when the engine is operating under high speed and high load conditions, the fuel is injected not only from the downstream injector but also from the upstream injector.
While such a fuel supply system provides improved fuel atomization, it fails to provide a compact arrangement. In other words, in order to have a sufficient spacing between the second fuel injector and the combustion chamber, the intake air passage would be fairly long. To shorten the intake air passage, JP-A-7-332208 teaches a structure in which at least a portion of the fuel injector is recessed into the air cleaner at the upstream end of the air intake passage.
With reference to FIG. 13, the structure of the fuel supply system described in JP-A-7-332208 is reproduced therein. As shown, a downstream injector 102 is placed downstream of a throttle valve 108 of a throttle body 106, which serves as an air intake path. Upstream of the throttle valve 108, an upstream injector 104 is placed inside of an air cleaner 100.
While the arrangement shown in FIG. 13 is an improvement over earlier configurations, this arrangement still has a number of drawbacks. For instance, fuel injected from the upstream injector generally will splash (hereinafter referred to as “bubble over”) outside of the air intake path due to air turbulence in the air cleaner. To address bubble over, it has been suggested that one should suppress the amount of fuel coming from the upstream injector or that one should move the upstream injector closer to an aperture of the air intake path.
Suppressing the amount of fuel coming from the upstream injector may result in a lean mixture being supplied to the engine. Moving the upstream injector closer to the aperture of the air intake path may decrease fuel atomization. Thus, both suggestions to correct bubble over lead to further complications and inefficiencies.